This invention relates to fuel cells and, in particular, to apparatus and methods of manufacturing the electrode assembly thereof.
A fuel cell is a device which directly converts chemical energy stored in hydrocarbon fuel into electrical energy by means of an electrochemical reaction. Generally, a fuel cell comprises an anode and a cathode separated by a member which serves itself to conduct electrically charged ions or is adapted to hold an electrolyte which conducts electrically charged ions. In order to produce a useful power level, a number of individual fuel cells are stacked in series with an electrically conductive separator plate separating the cells.
Each of the anode and the cathode, together with the ion-conducting member or member adapted to hold an ion-conducting electrolyte, comprise what will be referred to herein as the ion-conducting member electrode assembly (ICMEA). For different types of fuel cells, e.g., the proton exchange membrane (PEM), solid oxide (SOFC), molten carbonate (MCFC), phosphoric acid fuel cells (PAFC), etc., the ICMEAs are different, but all require the sandwich construction (planar, tubular or other) of the three components of the electrodes and member. While the discussion to follow illustrates the invention in terms of an assembly with a membrane ion-conducting member, as is used in PEM fuel cells, the principles of the invention are intended to extend to all types of fuel cells, electrochemical devices, and, in particular, the three-component construction of the ICMEAs of these cells.
In a PEM, the ion-conducting member is a membrane and the ICMEA is typically referred to as a membrane electrode assembly (MEA). Significant cost reduction is required in the current manufacturing costs of fuel cell components. Today's methods and systems for the manufacture of the MEA often require many steps causing them to be inefficient and thus expensive. Contributing to this inefficiency and expense is the current need to use solvents and other organics/dispersing agents when casting an MEA to realize a PEM of a desired energy yield. These solvents must be purchased and used throughout the manufacturing process. Aside from the costs associated with their purchase and use, there is an added expense involved in discarding the solvents due to environmental standards and regulations governing such disposal and human safety. Accordingly, eliminating solvents from the manufacturing process would not only reduce costs, but would also contribute to enhanced protection of the environment.
Another difficulty experienced in current practices for the production of MEAs is the inability to form the MEA as precisely as desired. Expensive reformulation steps are required to incorporate any process and design improvements. As a result, making MEAs of different size to accommodate fuel cells having different energy levels is made more difficult.
There are various methods to making an MEA structure. FIG. 1 shows a process for the manufacture of a MEA 10 according to today's conventional practice(s). An ion-conducting member, represented by the membrane 12, is positioned to receive each of the anode 14 and the cathode 16 comprised of their associated catalyst particles 18, 20. Formation of each electrode 14 and 16 begins by providing a desired substrate 21 (sacrificial or functional) to which a prepared “ink” 22, formed of catalyst particles, an ionomer solution and dispersing agents 24, is applied. The ink 22 is cast onto the substrate 21 according to a predetermined patterning chosen to accommodate the desired energy yield of the fuel cell.
Afterward, solvents 26 are applied to fix the ink 22 upon the substrate 21 according to the casting. The substrate 21 is then dried to form the electrode 14 or 16. Each electrode 14, 16 is then cut according to a predetermined size and later assembled with the membrane 12. Formation of each of the electrodes, i.e., the anode 14 and the cathode 16, takes place separately until the MEA 10 is finally formed by laminating, or, hot pressing each electrode 14, 16 into permanent contact with the membrane 10. In the case where a sacrificial substrate is used, a final removal step is required. This process also has a material loss in every step leading to a lower overall yield (<80%).
As may be seen, various stages of the illustrated process require that oversight, represented as quality control “QC”, exist in ensuring the quality of the process, and product produced thereby. As can be appreciated, it would be desirable to provide a more efficient method of associating the electrodes 14, 16 with the membrane 10, while at the same time reducing the amount of necessary oversight. Thus, a system and method for manufacturing a MEA which eliminates at least some of the steps represented at “X” would be desirable. Doing so would also provide a method and system better suited for the mass production of low-cost fuel cells.